The invention relates generally to digital filters, and to radar having digital filters.
The invention also relates to a digital filter having a plurality of paths and the parallel treatment of data in these paths.
It is known in the prior art to filter analog data using a plurality of parallel paths. Particularly, a plurality of parallel treatment paths are used to achieve, in analog form, the compression of radar pulses, when N is the number of paths used. The rate of compression of each path will be equal to u/N.sup.2 where u is the rate of compression.
In digital forms, dividing the treatment of the data between N parallel paths with a period of treatment N times slower would be an advantage. The rate of compression affected in each path would be equal to BT/N.sup.2, where B is the pass band of the signal, and T the width of a pulse. The rate of compression of the circuit, having N paths in parallel, is equal to B.times.T.
Previously, it was believed that for N parallel paths sliding was necessary for the digital filtering for each path of the data being filtered in each path and then to sum the results. This leads to a required calculating level proportional to N.sup.2. An advantage of the filter of the present invention is a reduction in the needed calculating power brought about by the separation of the paths by a discrete Fourier transform on 2N points. This gives the minimal number of points, specifically 2N-1, where the convolution of N points with the impulse response on N points of a filter can be correctly calculated by DFT (DFT).sup.-1 for the N points of the interval.
An object of the invention is to provide a digital filter having means for calculating the discrete Fourier transform, which is connected in parallel by a plurality of paths along which data is treated. The paths of treatment are connected to means for calculating the inverse discrete Fourier transform. The period of treatment along the parallel paths is N times less than the total input/output period of the device, N being equal to the number of samples treated simultaneously by the filter.
The invention will be better understood by a reference to the following description of different embodiments of the invention and the attached figures.